Recently, the use of a hands-free conversation function connected to a driver's cellular phone via Bluetooth communication has been widely used in a vehicle to ensure stability during car driving as well as a convenience function. The hands-free conversation is embodied through a microphone and a speaker of a vehicle, and thus is provided through an audio or navigation system (i.e., AVN or a head unit). However, the hands-free conversation may frequently maintain a call conversation state when a telephone conversation does not terminate normally due to a cellular phone itself or a wireless network environment. This causes a malfunction whereby media reproduction sound or navigation guidance voice is not output, or the use of a voice recognition function is restricted and causes confusion to a driver, thereby increasing danger of an accident.